(1) Field of the Invention
The present invention relates to dielectric materials and a method by which such dielectric materials are made.
(2) Description of the Prior Art
Dielectric materials may be used in many applications. Although not limited thereto in its use, dielectric materials have utility in microwave circuit boards. Also, dielectric materials may be used in capacitors.
One type of dielectric material was disclosed in a paper presented at IEEE/NEMA 1975 Electrical Electronics Insulation Conference at Boston, Mass. on Nov. 11, 1975, "EPSILAM 10- A New High Dielectric Constant Conformable Copper-Clad Laminate," M. Olyphant, Jr., D. D. Demeny, and T. E. Nowicki. EPSILAM 10, a product of the 3M Company, is believed to be a composite of poly(tetrafluoroethylene) (PTFE) and dielectric filler, the composite typically having a dielectric constant between 10 and 11 and being clad on both sides by copper foil.
Prior art dielectric materials exhibit numerous disadvantageous properties. Prior art dielectric materials, in general, absorb moisture in undesirable amounts. The absorption of moisture results in at least two serious problems: the electrical properties of the dielectric material are changed and the material may physically expand.
Moreover, prior art microwave dielectric materials may tend to have a non-uniform dielectric constant throughout the material. It is believed that this non-uniformity of dielectric constant is due, at least in part, to incomplete mixing of the dielectric material with the binder.
Futhermore, prior art dielectric materials may tend to have a relatively high energy dissipation factor.
Another type dielectric material used in microwave circuit boards is produced by Rogers Corporation, Rogers, Connecticut, and marketed under the trademark "RT/duroid". The "RT/duroid" dielectric material, which comprises PTFE and glass microfibers, has desirable strain relief properties but does not have a sufficiently high dielectric constant for some applications.
It is an object of the present invention to provide a dielectric material having a relatively high dielectric constant which is uniform throughout the material, relatively high tensile strength, desirable strain relief characteristics, low moisture absorption and an acceptable dissipation factor.